1. Field of the Invention
The invention relates to a vehicle seat frame.
2. Description of Related Art
Some vehicle seats are provided with a lifter device configured to adjust the height of a seat cushion. As illustrated in FIG. 4 and FIG. 5, in a lifter device described in Japanese Unexamined Patent Application Publication No. 2012-254777 (JP 2012-254777 A), a side frame 11 of a seat cushion, a front link 12, an upper rail 62 of a slide rail 61, and a rear link 13 constitute a four-bar linkage mechanism. A right rear lifter mechanism includes a collar 14 having a cylindrical portion 14a and a flange 14b. The cylindrical portion 14a of the collar 14 is passed through a through-hole of the rear link 13 and secured to the rear link 13 by welding. The outer peripheral surface of a portion of the cylindrical portion 14a of the collar 14, the portion being protruded from the through-hole of the rear link 13, is in sliding contact with the peripheral surface defining a hole of the side frame 11, and is prevented from coming off by a push nut 15, so that the rear link 13 is held so as to be rotatable with respect to the side frame 11. One end portion of a rear pipe 17 having an outer diameter that is slightly smaller than the inner diameter of the collar 14 is inserted in a through-hole of the collar 14, and the outer peripheral surface of the rear pipe 17 and the collar 14 are secured to each other by welding. A pinion gear 16 rotatably attached to the side frame 11 is meshed with a sector gear provided in the rear link 13. As the pinion gear 16 is rotated, the rear link 13 pivots in the front-rear direction about a shaft 63 attached to the upper rail 62, so that the side frame 11 moves up and down via the collar 14. At this time, the front link 12 moves in accordance with the movement of the rear link 13, so that the side frame 11 moves up and down while the side frame 11 is kept substantially parallel to the slide rail 61.
In a technology described in JP 2012-254777 A, the outer diameter of the rear pipe 17 that couples the right and left collars 14 to each other is smaller than the outer diameter of each collar 14. In order to avoid a shortage of the torsional strength of a welded spot where the collar 14 and the rear pipe 17 are secured to each other by welding and a shortage of the bending strength of the rear pipe 17, the rear pipe 17 needs to have a large wall thickness. This increases the weight of the rear pipe 17.